Single aperture opening beverage cans utilize a single large hole to admit air for venting the dispensed liquid. Examples are given in U.S. Pat. Nos. 4,210,257; 5,007,554; 4,416,389; 4,148,410; 4,465,204; and 4,361,251, the disclosures of which are incorporated herein by reference.
In order to produce a more efficient, controlled flow rate, it is desirable to have a second hole that is diametrically opposite the first aperture. This is especially advantageous for carbonated and malt beverages such as beer. This enables users to control rate of direct consumption, pouring and consequent foam head. Prior to large holed single aperture lift tab cans, beer cans were typically opened with "Church Keys", applied first to one side, then to the opposite side of the can top. This was done in order to increase the flow rate of the beverage and for better control of the liquid stream.